Defibrillator charging

ABSTRACT

Systems and methods related to the field of cardiac resuscitation, and in particular to devices for assisting rescuers in performing cardio-pulmonary resuscitation (CPR).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/091,694, filed Apr. 6, 2016, which is a continuation of U.S. patentapplication Ser. No. 13/025,327, filed on Feb. 11, 2011, which claimspriority to U.S. Provisional Patent Application No. 61/304,119, filed onFeb. 12, 2010, and U.S. Provisional Patent Application No. 61/307,690,filed on Feb. 24, 2010, the entire contents of each of which are herebyincorporated by reference.

TECHNICAL FIELD

This document relates to cardiac resuscitation, and in particular tosystems and techniques for assisting rescuers in performingcardio-pulmonary resuscitation (CPR).

BACKGROUND

The heart relies on an organized sequence of electrical impulses to beateffectively. Deviations from this normal sequence is known as“arrhythmia.” Certain medical devices include signal processing softwarethat analyzes electrocardiography (ECG) signals acquired from a medicalpatient (e.g., a victim at a scene of an emergency) to determine when acardiac arrhythmia such as ventricular fibrillation (VF) or shockableventricular tachycardia (VT) exists. These devices include automatedexternal defibrillators (AEDs), ECG rhythm classifiers, and ventriculararrhythmia detectors. An AED is a defibrillator—a device that deliverscontrolled electrical shock to a patient—while being relatively easy touse, such as by providing verbal prompts to a provider of care to “talk”the provider through a process of evaluating a patient for, attachingthe patient to, and activating, AED therapy. Certain of the medicaldevices just discussed are also capable of recognizing the two distinctcardiac waveforms: VT and VF.

VT is a tachydysrhythmia that originates from a ventricular ectopicfocus, characterized by a rate that is typically greater than 120 beatsper minute and wide QRS complexes. VT may be monomorphic (typicallyregular rhythm originating from a single focus with identical QRScomplexes) or polymorphic (unstable, may be irregular rhythm, withvarying QRS complexes). An example rhythm for an unstable VT isillustrated in FIG. 1A. Depending on the rate and the length of timethat the VT has been sustained, a heart in the VT state may or may notproduce a pulse (i.e., pulsatile movement of blood through thecirculatory system). The cardiac activity in the VT state still has somesense of organization (note that the “loops” are all basically the samesize and shape). If there is no pulse associated with this VT rhythm,then the VT is considered to be unstable and a life threateningcondition. An unstable VT can be treated with an electrical shock ordefibrillation.

Supraventricular tachycardia (SVT) is a rapid heartbeat that beginsabove the heart's lower chambers (the ventricles). SVT is an abnormallyfast heart rhythm that begins in one of the upper chambers of the heart(atria), a component of the heart's electrical conduction system calledthe atrioventricular (AV) node, or both. Although SVT is rarelylife-threatening, its symptoms, which include a feeling of a racingheart, fluttering or pounding in the chest or extra heartbeats(palpitations), or dizziness can be uncomfortable.

VF is usually an immediate life threat. VF is a pulseless arrhythmiawith irregular and chaotic electrical activity and ventricularcontraction in which the heart immediately loses its ability to functionas a pump. VF is the primary cause of sudden cardiac death (SCD). Anexample rhythm for VF is illustrated in FIG. 1B. This waveform does nothave a pulse associated with it. There is no organization to this rhythm(note the irregular size and shape of the loops). The pumping part ofthe heart is quivering like a bag of worms, and it is highly unlikelythat this activity will move any blood. The corrective action for thisrhythm is to defibrillate the heart using an electrical charge.

A normal heart beat wave starts at the sinoatrial node (SA node) andprogresses toward the far lower corner of the left ventricle. A massiveelectrical shock to the heart can correct the VF and unstable VTrhythms. This massive electrical shock can force all the cardiac cellsin the heart to depolarize at the same time. Subsequently, all of thecardiac cells go into a short resting period. The hope is that thesinoatrial node (SA node) will recover from this shock before any of theother cells, and that the resulting rhythm will be a pulse-producingrhythm, if not normal sinus rhythm.

Many AEDs implement algorithms to recognize the VT and VF waveforms byperforming ECG analyses at specific times during a rescue event of apatient using defibrillation and cardio-pulmonary resuscitation (CPR).The first ECG analysis is usually initiated within a few seconds afterthe defibrillation electrodes are attached to the patient. SubsequentECG analyses may or may not be initiated, based upon the results of thefirst analysis. Typically, if the first analysis detects a shockablerhythm, the rescuer is advised to deliver a defibrillation shock.Following the shock delivery, a second analysis can be initiatedautomatically to determine whether the defibrillation treatment wassuccessful or not (i.e., the shockable ECG rhythm has been converted toa normal or other non-shockable rhythm). If this second analysis detectsthe continuing presence of a shockable arrhythmia, the AED advises theuser to deliver a second defibrillation treatment. A third ECG analysismay then be executed to determine whether the second shock was or wasnot effective. If a shockable rhythm persists, the rescuer is thenadvised to deliver a third defibrillation treatment.

Following the third defibrillator shock or when any of the analysesdescribed above detects a non-shockable rhythm, treatment protocolsrecommended by the American Heart Association and European ResuscitationCouncil require the rescuer to check the patient's pulse or to evaluatethe patient for signs of circulation. If no pulse or signs ofcirculation are present, the rescuer can be directed to perform CPR onthe victim for a period of one or more minutes. The CPR includes rescuebreathing and chest compressions. Following this period of CPR, the AEDreinitiates a series of up to three additional ECG analyses interspersedwith appropriate defibrillation treatments as described above. Thesequence of three ECG analyses/defibrillation shocks followed by 1-3minutes of CPR, continues in a repetitive fashion for as long as theAED's power is turned on and the patient is connected to the AED device.Typically, the AED provides audio prompts to inform the rescuer whenanalyses are about to begin, what the analysis results were, and when tostart and stop the delivery of CPR.

Many studies have reported that the discontinuation of precordialcompression can significantly reduce the recovery rate of spontaneouscirculation and 24-hour survival rate for victims. Thus, it is useful torecognize abnormal heart rhythms during chest compressions. There isrecent clinical evidence showing that performing chest compressionsbefore defibrillating the patient under some circumstances can bebeneficial. Specifically, it is clinically beneficial to treat a patientwith chest compressions before defibrillation if the response times ofthe medical emergency system result in a delay of more than fourminutes, such that the patient is in cardiac arrest for more than fourminutes. Chest compression artifact rejection can employ spectralanalysis of the ECG, defibrillation success prediction, and therapeuticdecision-making typically specify a set of parameters in the ECGfrequency spectrum to be detected. For example, U.S. Pat. No. 5,683,424compares a centroid or a median frequency or a peak power frequency froma calculated frequency spectrum of the ECG to thresholds to determine ifa defibrillating shock is necessary.

Unfortunately, existing AEDs require batteries able to deliver largeamounts of current due to the charging requirements of defibrillatorhigh voltage capacitors. This results in batteries that are excessive inboth size and weight that limit both their portability, convenience, andin the case of external, wearable defibrillators such as the LifeVest(ZOLL Medical, Chelmsford, Mass.) their wearability and comfort. Inaddition, batteries continue to be the least reliable element of theAEDs currently manufactured, with regular recalls resulting frommanufacturing defects as well as normal end-of-life degradation thatalways occurs with batteries, but are particularly troublesome forlife-saving equipment.

SUMMARY

The systems and techniques described here relate to control of thecharging of a defibrillator, such as an AED, so as to makedefibrillation readily available to an operator of the defibrillator,and also to extend battery life of the defibrillator. For example, asystem may make a determination, by performing an ECG analysis while arescuer is giving CPR, or whether a defibrillating pulse is appropriate,and may charge a capacitor or other energy providing mechanism while theuser is still performing the CPR. As a result, the energy may already bestored when the time comes for the user to provide a shock.

In one implementation, a method for providing electrical therapy to apatient includes analyzing one or more electrocardiogram (ECG) signalsfrom the patient. The method also includes selectively charging adefibrillation device based on the analysis of the one or moreelectrocardiogram (ECG) signals while chest compressions are beingadministered to the patient.

Embodiments can include one or more of the following. The method caninclude providing a defibrillating shock from the charged defibrillatingdevice after chest compressions have ceased being administered. Themethod can include providing a defibrillating shock from the chargeddefibrillating device while chest compressions are being administered.The method can also include selectively charging the defibrillationdevice includes only charging the defibrillation device if adefibrillating shock to the victim's heart is determined, from theanalysis of the ECG signals, to be suitable therapy. The method can alsoinclude, before providing the defibrillating shock, determining whethera defibrillating shock to the victim's heart is suitable therapy basedon the analyzed one or more ECG signals. Selectively charging thedefibrillation device can include determining, based on the analysis ofthe one or more ECG signals, whether to charge the defibrillation deviceor to instruct the user to continue chest compressions without chargingthe defibrillation device. Selectively charging the defibrillationdevice can include determining a rate of charge based on the one or moreECG signals. Selectively charging the defibrillation device can includedetermining a rate of charge based on a determined amount of time thatremains until the end of a current chest compression cycle. Selectivelycharging the defibrillation device can include determining a totalamount of charge based on the one or more ECG signals. Selectivelycharging the defibrillation device can include imposing one or moresafety interlocks to prevent accidental discharge of the defibrillationdevice during charging of the defibrillation device. Analyzing the oneor more ECG signals can include calculating an amplitude magnitudespectrum area (AMSA) value and selectively charging the defibrillationdevice can include selectively charging the defibrillation device ordetermining a rate of charge based on the calculated AMSA value.Selectively charging the defibrillation device can include charging thedefibrillation device over a time period of at least about 30 seconds.Selectively charging the defibrillation device can include charging thedefibrillation device over a time period of at least about 1 minute.

In some additional implementations, an external defibrillator forproviding automatically controlled shock to victims of heart problemsincludes an electrical energy storage source and a temporary electricalstorage device in electrical connection with the electrical energystorage source and capable of delivering a defibrillating shock to ahuman victim. The defibrillator also includes a controller programmed toanalyze one or more electrocardiogram (ECG) signals and to performcharging of the temporary electrical storage device from the electricalenergy storage source while directing chest compressions of the victim.

Embodiments can include one or more of the following.

The external defibrillator can also include a charging device to chargethe temporary electrical storage device in response to commands from thecontroller. The controller can be further programmed to start chargingthe temporary electrical storage device at a time before the end of acurrent chest compression cycle that is determined to substantiallymatch a time needed to fully charge the temporary electrical storagedevice. The temporary electrical storage device can be a capacitor. Theexternal defibrillator can also include electrode pads that areconnected to the defibrillator, include adhesive material for adheringto the victim, and are arranged to deliver a defibrillating shock fromthe temporary electrical storage device to the victim. The controllercan be further programmed to selectively charge the temporary electricalstorage device only if a defibrillating shock to the victim's heart isdetermined, from the analysis of the ECG signals, to be suitabletherapy. The controller can be further programmed to determine whether adefibrillating shock to the victim's heart is suitable therapy based onthe analyzed one or more ECG signals. The controller can be furtherprogrammed to determine based on the analysis of the one or more ECGsignals, whether to charge the temporary electrical storage device or toinstruct the user to continue chest compressions without charging thetemporary electrical storage device. The controller can be furtherprogrammed to determine a rate of charge for charging the temporaryelectrical storage device based on the one or more ECG signals. Thecontroller can be further programmed to determine a rate of charge forcharging the temporary electrical storage device based on a determinedamount of time that remains until the end of a current chest compressioncycle. The controller can be further programmed to determine a totalamount of charge for charging the temporary electrical storage devicebased on the one or more ECG signals. The external defibrillator canalso include one or more safety interlocks to prevent accidentaldischarge of the temporary electrical storage device during charging ofthe temporary electrical storage device. The controller can be furtherconfigured to analyze the one or more ECG signals by calculating anamplitude magnitude spectrum area (AMSA) value and selectively chargethe temporary electrical storage device at a variable charging speedbased on the calculated AMSA value.

Such features may provide one or more advantages in some particularimplementations. For example, a defibrillator may enable a rescuer tomove quickly from providing CPR to delivering a defibrillating shock,and then to continue with lifesaving efforts. Minimizing the time duringwhich treatment has ceased may be an important factor for survival of apatient, particularly where lay responders are providing care as abridge to the arrival of professional responders. Also, battery life fora defibrillator may be extended by charging an energy delivery deviceonly when it is likely to be needed, and to the extent it will beneeded. As a result, a defibrillator may be more likely to be usablelonger, and thus available when later care may be needed. Also, the lifeof the defibrillator may be extended by reducing wear and tear on thedevice (e.g., on the capacitor) by charging an energy delivery deviceonly when it is likely to be needed.

Other features and advantages will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a magnitude versus time plot of a ventricular tachycardia(VT) rhythm.

FIG. 1B is a magnitude versus time plot of a ventricular fibrillation(VF) rhythm.

FIG. 2 is a diagram of one implementation including an automaticelectronic defibrillator (AED) and a multiple lead electrocardiograph(ECG) device.

FIG. 2A is a diagram of the AED of FIG. 2.

FIGS. 3A and 3B are examples of ECG analysis and charging cycles.

FIG. 4A is a flow chart showing actions taken to charge a defibrillationdevice during chest compressions associated with a CPR interval.

FIG. 4B is a flow chart showing actions taken to charge a defibrillationdevice using different current levels that are selected based on thelikelihood of a shockable rhythm being observed.

FIG. 4C is a flow chart showing actions taken to adaptively charge adefibrillation device using different current levels based on thelikelihood of a shockable rhythm being observed.

FIG. 4D is a flow chart showing actions taken to adaptively charge adefibrillation device to a level selected based on ECG analysis.

FIG. 5A is a diagram of and ECG signal.

FIG. 5B is a diagram of a CPR acceleration signal showing strongcross-correlation with the ECG signal.

FIG. 6A is a diagram of and ECG signal.

FIG. 6B is a diagram of a CPR acceleration signal showing lowcross-correlation with the ECG signal.

DETAILED DESCRIPTION

This description discusses systems and techniques for providingdefibrillation energy in a controlled manner. In general, such energyneeds to be built up, such as by charging a capacitor, and that build upof energy may take an appreciable length of time. Using the techniquesdiscussed here, a system can analyze a patient's needs in advance of thetime to delivery defibrillation pulse (e.g., while a rescuer isperforming chest compressions) and can begin charging a capacitor orother appropriate energy delivery mechanism sufficiently in advance ofthe time that a shock will be needed, so that the shock can be deliveredas soon as it is needed.

Referring now to FIG. 2, an AED 10 is shown that may be used to providea defibrillation shock at an appropriate time. In the figure, whichshows an example implementation, a rescuer uses an AED 10 toautomatically monitor a victim during cardiac resuscitation. The AED 10uses measured ECG signals to monitor the victim's heart, and charges thedefibrillation device within the AED while the victim is resuscitatedusing chest compressions techniques. In some examples, the manner inwhich the defibrillation device is charged (e.g., the rate of charge,the total amount of charge stored) can be based on the measured ECGsignals. Advantageously, charging the defibrillation device during CPRchest compressions reduces the amount of time that the victim is notreceiving chest compressions because, if a shockable rhythm exists, thedevice is armed and ready to deliver the shock as soon as the rescuercompletes the chest compressions.

The AED 10 includes a speaker 16, a display screen 18, ananalog-to-digital converter 20, a processor 22, and a defibrillatorpulse generator 24. The analog-to-digital converter 20 is connected to aset of ECG leads that are in turn attached to the victim. The ECG leadspass signals to the processor 22 for monitoring the electrical rhythmsof the victim's heart. The converter 20 sends the signals from the ECGleads to the processor 22. The processor 22 monitors the victim's heartfor dangerous rhythms using the ECG signals while the victim isresuscitated using chest compressions techniques.

If the AED 10 detects a dangerous heart rhythm, the AED 10 generates analarm signal. The alarm signal is noticeable to the rescuer. The AED 10can generate a defibrillating shock to the victim when the rescuerissues a command to the AED 10 directing such a shock. Thedefibrillating shock is intended to remedy the dangerous rhythm of thevictim's heart.

The AED 10 also includes a charging module 19 that is configured tocharge the AED during chest compressions. The module 19 can adaptivelycharge the AED based on monitored ECG signals. In some examples, thedefibrillator is pre-charged only if a shockable rhythm is likely toexist as determined by analysis of the monitored ECG signals. In someadditional examples, the level of charge for the device is determinedand set based on the monitored ECG signals. In some additional examples,the method of charging (e.g., the rate of charge) varies based on themonitored ECG signals in an effort to conserve power. For example, iftime allows, a capacitor may be charged more slowly than it normallywould in order to conserve power, but still ensure that the capacitorwill reach its full charge just as the defibrillator is needed by therescuer.

The AED 10 uses a rhythm advisory method for a) quantifying thefrequency-domain features of the ECG signals; b) differentiating normaland abnormal ECG rhythms, such as VF; c) detecting the onset of abnormalECG rhythms; and d) making decisions about the physiological states ofthe heart. This frequency-domain measure can be reliable with or withoutthe presence of the chest compression artifact in the ECG signals. TheAED 10, after identifying the current physiological state of the heart,can make a decision about appropriate therapeutic action for the rescuerto make and communicate the action to the rescuer using the speaker 16and the display screen 18.

The AED 10 may incorporate functionality for performing additionaltherapeutic actions such as chest compressions, ventilations, ordelivery of intravenous solution-containing metabolic or constitutivenutrients. Based on the results of the analysis of the rhythm advisorymethod, the AED 10 may automatically deliver the appropriate therapy tothe patient.

The AED 10 may also be configured in “advisory” mode wherein the AED 10will prompt the caregiver after the AED 10 has made a determination ofthe best therapy, and acknowledgement by the caregiver/device operator,in the form of a button press or voice-detected acknowledgement, isrequired before therapy is delivered to the patient.

The AED 10 analyzes the ECG signals to predict defibrillation success aswell as to decide whether it is appropriate to defibrillate or todeliver an alternative therapy such as chest compressions, drugs such asepinephrine, constitutive nutrients such as glucose, or other electricaltherapy such as pacing.

In some examples, one or more therapeutic delivery devices 30automatically deliver the appropriate therapy to the patient. Thetherapeutic delivery devices 30 can be, for example, a portable chestcompression device, a drug infusion device, a ventilator and/or a devicethat includes multiple therapies such as defibrillation, chestcompression, ventilation and drug infusion. The therapeutic deliverydevices 30 are physically separate from the defibrillator AED 10, andcontrol of the therapeutic delivery devices 30 may be accomplished by acommunications link 32. The communications link 32 may take the form ofa cable but preferably the link 32 is via a wireless protocol.

In other examples, control and coordination for the overallresuscitation event and the delivery of the various therapies may beaccomplished by a device 34 or processing element that is external tothe AED 10. For instance, the device 34 may download and process the ECGdata from the AED 10; analyze the ECG signals, perform relevantdeterminations like those discussed above and below based on theanalysis, and control the other therapeutic devices 30, including theAED 10. In other examples, the AED 10 may perform all the processing ofthe ECG, including analyzing the ECG signals, and may transmit to thecontrol device 34 only the final determination of the appropriatetherapy, whereupon the control device 34 would perform the controlactions on the other linked devices 30.

Chest compression artifacts can be separated from the ECG signalcomponents, making it possible for the AED 10 to process the ECG signalwithout halting the processing during chest compressions. Exemplarymethods for analyzing the ECG signal to determine if a shockable rhythmexists are described, for example, in U.S. Pat. No. 7,565,194, titled“ECG Rhythm Advisory Method,” the contents of which are herebyincorporated by reference in their entirety.

It has been recognized that good chest compressions during CPR isessential to saving more victims of cardiac arrest. The compression raterecommended by the American Heart Association in its guidelines isgreater than 100 compressions per minute. Many studies have reportedthat the discontinuation of chest compressions, such as is commonly donefor ECG analysis and charging of a defibrillator, can significantlyreduce the recovery rate of spontaneous circulation and 24-hour survivalrate. Because of safety issues with delivery of a high voltagedefibrillation shocks with voltages of 1000-2000 volts, rescuers aretaught to cease chest compressions and remove their hands from thevictim's chest before initiating the defibrillation shock. By analyzingECG signals during chest compressions as a mechanisms to permit earliercharging of an energy delivery device (e.g., a capacitor) in adefibrillator device, the gaps in providing chest compressions can bereduced, and patient care increased.

FIG. 3A shows an example of an ECG analysis and charging cycle in whichcharging of a defibrillator device starts after a CPR interval hasended. As shown in the figure, in operation of some AED devices, therescuer is instructed to perform chest compressions for a two minute CPRinterval 300 after which the rescuer is instructed to pause his or herperformance of CPR 304. At this point, the rescuer removes his or herhands from the victim, ECG analysis is performed, and the defibrillatordevice is charged (interval 302). As such, a time period elapses (timeperiod 302) during which the rescuer is not delivering chestcompressions to the victim. This elapsed time period before delivery ofthe shock 307 can be, for example, about 10 seconds—of which a portionis devoted to performing the ECG analysis and a portion is devoted tocharging the defibrillation device. While methods exist for processingECG signals without halting the processing during CPR chestcompressions, a time period may still elapse between the cessation ofchest compressions and availability of an adequate charge for deliveringa shock.

FIG. 3B shows an example of an ECG analysis and charging cycle in whichcharging of a defibrillator device starts before a CPR interval hasended. The CPR interval can be based on a length of time ofadministration of chest compressions (e.g., as shown in FIG. 3B), atotal number of chest compressions, a total number of effective chestcompressions based on depth or rate of the compression, a total lengthof time of effective chest compressions, or can be variable based on oneor more observed factors such as the ECG analysis. The CPR interval canadditionally be updated by software or firmware to handle different CPRprotocols such that the device is charged and the defibrillation therapyis delivered according to the protocol. As shown in the figure, inoperation methods described herein, the defibrillation device is chargedwhile the rescuer is providing the CPR chest compressions. Similar tothe method described with respect to FIG. 3A, the rescuer is instructedto perform chest compressions for a two minute CPR interval 308. Duringthe two minute CPR interval, ECG analysis is performed and thedefibrillator device is charged (interval 310). After the CPR intervalis complete, the rescuer is instructed to pause CPR 312, and shock 314can be delivered almost immediately to the victim because thedefibrillator device has already had time to charge. Because thedefibrillator device is fully charged before the rescuer ceases chestcompressions, the time period during which the rescuer is not deliveringchest compressions to the victim can be greatly reduced and the shockcan be delivered immediately or almost immediately after chestcompressions are completed. For example, the elapsed time between theend of the CPR interval and the delivery of the shock (if a shockablerhythm exists) can be less than about 5 seconds (e.g., less than about 5seconds, less than about 3 seconds, less than about 2 seconds, less thanabout 1 second, less than about ½ a second). In some embodiments, thelength of time between the rescuer ceasing chest compressions anddelivery of the shock can be simply based on the amount of time therescuer spends locating and pressing a button on the AED device thatcauses the AED device to deliver the shock to the victim.

In some additional embodiments, the AED device may utilize a briefperiod of time (e.g., while the rescuer locates and presses the button)after the rescuer ceases chest compressions to reconfirm thedesirability of delivering the shock to the victim. For example, arescuer can be instructed to visually inspect and confirm that ashockable rhythm exists and/or the AED device can continue to collectand analyze ECG signals (in the absence of chest compressions resultingin less artifacts in the ECG signal) to re-confirm the desirability ofdelivering the shock. In general, a time period for re-confirmationbased on analysis of an ECG signal without chest compression artifactscan be brief (e.g., less than about 5 seconds, less than about 3seconds, less than about 2 seconds). The time period for re-confirmationcan be based on physiological characteristics (e.g., heart rate that isfast or slow) and/or a desired confidence level for the ECG analysis.

Because of safety issues with charging the defibrillation device to avoltage of 1000-2000 volts while the rescuer is in contact with thevictim, safety interlocks can be included in a defibrillator device toensure that the voltage is not discharged before the rescuer removes hisor her hands from the victim. The defibrillator safety interlocks caninclude one or more software-controlled-hardware and/or softwaremechanisms that prevent the defibrillator from accidentally dischargingoutside of the unit. In order for the defibrillator to deliver a shock,the AED device confirms that a variety of software and hardware statesare met during the charging process. Once the defibrillator reaches afull level of charge, a therapy button is enabled. Enabling the therapybutton removes a final hardware safety interlock and selects the outputfor the therapy charge to the patient connector instead of the internalresistor network used to dissipate charge when a shock is not delivered.Once enabled, a rescuer presses the therapy button and the AED registersthe press which closes a therapy delivery relay and delivers thedefibrillation pulse. The safety interlocks control the enablement ofthe therapy button and a do not allow the rescuer to deliver a shock tothe victim until other actions occur that disable the safety interlocks.

In some additional methods, an electrically insulating protection layerextends over the surface of the patient so that manual compressions maycontinue safely and unabated during the charging of the defibrillationdevice and delivery of the defibrillation shock. An exemplaryelectrically insulating protection layer is described, for example, inU.S. Pat. No. 6,360,125, which is incorporated by reference herein inits entirety.

In some embodiments, the period for administration of chest compressionsis not preset, rather the period can be variable based on the observedEGC signals. ECG analysis may start while CPR chest compressions arebeing administered. When the AED device determines that a shockablerhythm exists based on the ECG signals or otherwise makes adetermination that the appropriate therapy would be to deliver thedefibrillation shock, the AED device can begin charging. CPR chestcompressions continue while the device is charging. The AED device canoptionally instruct the rescuer of an amount of time that he/she shouldcontinue to administer chest compressions based on the length of timeused to charge the defibrillator device. Once the device is fullycharged, the rescuer can be the victim.

FIG. 4A is a flow chart showing actions taken to charge a defibrillationdevice during chest compressions associated with a CPR interval. Asnoted above, charging the defibrillation device in addition to analyzingan ECG signal during chest compressions can provide the advantage ofreducing the amount of time that a rescuer is not administering chestcompressions to the victim. In general, an interval (e.g., a set lengthof time) is set for the administration of chest compressions. Duringthis interval, the system analyzes an ECG signal and charges thedefibrillation device. Safety interlocks are enabled that preventaccidental dissipation of the charge in the defibrillation device duringthe CPR chest compression interval. At the end of the CPR interval, adecision of whether to shock the victim is made based on the ECG signalanalysis, and the stored charge is either administered to the victim ordissipated internally.

The example process here begins at box 402, where the AED analyzes anECG signal to determine if a shockable rhythm is present in the victim.The ECG signal is measured while chest compressions are beingadministered to the victim. As such, the AED separates the chestcompression artifact from the ECG signal components to process the ECGsignal without halting the processing during CPR chest compressions(e.g., as described in U.S. Pat. No. 7,565,194).

At box 404, the AED determines if the current time is near the end ofthe CPR interval (e.g., within about 10-30 seconds of the end of the CPRinterval). Exemplary CPR intervals can be between 2 and 5 minutes (e.g.,2 minutes, 3 minutes, 4 minutes, and 5 minutes). If the current timewithin a determined window for performing chest compressions is not nearthe end of the CPR interval, the AED device continues to analyze the ECGsignals (box 402). If the current time is near the end of the CPRinterval, the AED enables safety interlocks at box 406 (though theinterlocks may be enabled even before this time).

As the chest compressions continue, the AED begins charging thedefibrillation device at box 408 with the safety interlocks enabled. Theamount of time needed to charge the defibrillation device can vary basedon the current used to charge the device and the total amount of chargedesired. As such, the system begins charging the defibrillation devicein advance of the end of the CPR interval such that the defibrillationdevice will be fully charged at the end of the CPR interval. Forexample, a window for performing CPR can be determined when the CPRcycle begins, a time for charging the defibrillation device can belooked up or otherwise determined, and the system may be programmed tocheck, at a time in advance of the end of the window that substantiallycorresponds to the charging time, for whether a shockable rhythm ispresent

At box 410, the AED performs a final analysis of the ECG signal todetermine if a shockable rhythm is present in the victim. Exemplarymethods for analyzing the ECG signal to determine if a shockable rhythmexists are described, for example, in U.S. Pat. No. 7,565,194, titled“ECG Rhythm Advisory Method,” the contents of which are herebyincorporated by reference in their entirety. If a shockable rhythm isnot observed, at box 422, the AED instructs the rescuer to continuechest compressions. Thus, if a shockable rhythm does not exist, thevictim receives uninterrupted chest compressions. Such chestcompressions may not place the heart back into normal operation, butthey may nonetheless maximize perfusion of blood through the heart untila more highly-trained rescuer can arrive and take over.

At box 424, the AED dissipates the charge from the defibrillation devicewithout delivering a shock to the victim. For example, the AED candissipate the stored charge using a resistor network inside the AEDdevice such that the charge can be dissipated without requiring therescuer to discontinue chest compressions. The dissipation may occur bydumping the charge, for example. The charge may also be “recycled” backinto a battery on the device so as to extend the battery life.

If a shockable rhythm is observed, at box 414, the AED device instructsthe rescuer to discontinue chest compressions. For example, the AEDdevice can provide audible instructions to the rescuer via a speakerand/or can provide a visual instruction to the rescuer via a displaydevice. At box 416, the AED disables the safety interlocks, thus makingit possible for the shock to be delivered through electrodes that areattached to the victim.

At box 418, the AED device delivers the defibrillation shock to thevictim. Such delivery may occur in response to the rescuer pressing abutton on the AED to provide a command to delivered the shock. The shockmay also be delivered automatically, such as after the AED voices acommand to stand clear of the victim. The shock is delivered withoutsignificant delay after the cessation of chest compressions because thedevice has been previously pre-charged while the chest compressions werebeing administered.

At box 420, the AED device instructs the user to resume chestcompressions. This initiates another CPR cycle during which a similarECG analysis will be performed. The process just described may thus berepeated until a shock succeeds in placing the victim's heart roughlyback into a normal operating mode, or until additional caregivers arriveto attempt different resuscitation approaches.

In some embodiments, a reconfirmation of the desirability to deliver thedefibrillation shock to the victim is performed after the rescuer ceaseschest compressions. Because the re-confirmation is performed when therescuer is not delivering chest compressions, the ECG signals analyzedby the AED device during the reconfirmation are expected to be lessnoisy and have less artifacts because artifacts from the chestcompressions are no longer present. As such, an ECG analysis may havehigher degree of confidence. In general, as described above, a timeperiod for re-confirmation based on analysis of an ECG signal withoutchest compression artifacts can be brief (e.g., less than about 5seconds, less than about 3 seconds, less than about 2 seconds).

In some embodiments, the AED device can determine whether to perform areconfirmation analysis based on one or more factors associated with theprior EGC analysis such as a certainty value. For example, if the priorEGC analysis results in a high certainty that delivering thedefibrillation shock to the victim is the appropriate therapy (e.g., ahigh certainty of conversion to a perfusing rhythm) then the AED maydeliver the shock nearly immediately after the rescuer ceases chestcompressions (e.g. without a reconfirmation period). On the other hand,if the prior EGC analysis has a lower certainty that delivering thedefibrillation shock to the victim is the appropriate therapy then theAED may perform a reconfirmation analysis before making a finaldetermination of whether to deliver the defibrillation shock.Additionally or alternatively a determination of whether to perform areconfirmation analysis can be based on a confidence value associatedwith the level of confidence that the EGC signal analysis is correct.For example, if the signal is extremely noisy and has a large presenceof artifacts, the confidence of the analysis may be lower making itdesirable to reconfirm the analysis in the absence of the chestcompressions.

FIG. 4B is a flow chart showing actions taken to charge a defibrillationdevice using different current levels that are selected based on thelikelihood of a shockable rhythm being observed. Portable AED devicesmay be powered by a battery or other power supply having a limitedlifetime. In order to conserve power for future uses of the AED deviceor for the administration of multiple shocks to a single victim, variouscharging algorithms can be used. In some examples, an AED device makes adetermination of whether a shockable rhythm exists in the victim andonly charges the defibrillator device if a shockable rhythm exists. Sucha charging algorithm conserves power because if a shockable rhythm isnot observed, the AED device does not charge the defibrillator and thendump or dissipate the charge.

The example process begins at box 425, where the AED analyzes an ECGsignal while chest compressions are being administered to a victim todetermine if a shockable rhythm is likely to be present in the victim atthe end of the CPR interval (e.g., as described in U.S. Pat. No.7,565,194). At box 426, the AED determines if a shockable rhythm islikely to be present in the victim at the end of the CPR interval. Whilethe CPR interval will continue regardless of the outcome of theanalysis, the determination is used to decide whether to begin chargingthe defibrillator device. The time at which to make such a determinationmay be set by a determination of how long it will take to charge thedefibrillator device. When different possible rates of charge areavailable to the system, and maximum time charge can be set for the ECGanalysis, a rate of charge may be determined, and then the actualcharging may begin at a time preceding the end of CPR that issubstantially the amount of time the charge will take at the computedrate of charge.

A threshold for determining whether to pre-charge the defibrillator canbe different from a threshold used to determine whether to administer ashock to the victim. For example, because the determination is used todecide whether to pre-charge the AED device, a lower threshold may beused such that the device will be fully charged at the end of the CPRinterval if a shock may be administered. For example, an accuracymeasure can be used to set the thresholds. For example, an observedsignal resulting in a high accuracy value (e.g., a confidence of greaterthan about 90%) can be used as to set a threshold for determiningwhether to administer a defibrillation shock to the victim while a lowerconfidence (e.g., a confidence of 50% or greater) can be used to set athreshold for determining whether to begin charging the defibrillationdevice. For example, an AMSA number that is associated with a certainaccuracy level in predicting a successful conversion can be used to setthe thresholds for deciding whether to pre-charge the defibrillator, therate of charging the defibrillator, and whether to administer thedefibrillation shock. This AMSA number can be customized based on arequest of the rescuer or the medical director. For example, an AMSAnumber that is associated with a accuracy level of 90% or greater (e.g.,90% or 95%) in predicting a successful conversion can be used to set thethreshold for administering a defibrillation shock and an AMSA numberthat is associated with a accuracy level of 70% or greater (e.g., 70%,80%, 90%) in predicting a successful conversion can be used to set thethreshold for deciding whether to pre-charge the defibrillator. In otherexamples, an AMSA number that is associated with an accuracy level of70% or greater (e.g., 70%, 80%, 90%) in predicting a successfulconversion can be associated with the fastest possible rate in chargingthe defibrillator; The lower value the AMSA number is, the rate ofcharging is set to (e.g., half speed in charging when an AMSA numberassociated with an accuracy level of 50% is observed). In someembodiments, other predictors of conversion success (e.g., SCE) can beused.

If a shockable rhythm is not likely to be present in the victim at theend of the CPR interval, the AED continues to receive and analyze theECG signals. At box 428 near the end of the CPR cycle, the AED deviceperforms a final analysis of the ECG signal to determine whether ashockable rhythm exists. This second determination of whether ashockable rhythm exists serves as a confirmation that a shockable rhythmstill does not exist, so that a rescuer does not forego providing ashock to the victim in a situation where the patient's condition haschanged in a manner that would make a shock would be beneficial.

In contrast, if the system determines that a shockable rhythm is likelyto exist, at box 427, the AED pre-charges the defibrillation device.This charging occurs while the rescuer is administering the CPR chestcompressions. At box 428 near the end of the CPR cycle, the AED deviceperforms a final analysis of the ECG signal.

At box 429, the AED device determines whether a shockable rhythm exists.This second determination of whether a shockable rhythm exists serves asa confirmation that a shockable rhythm still exists, so that a rescueris not led to give a shock to a patient when the patient's condition haschanged in a manner that would make the shock essentially futile. Adifferent threshold can be used for the determination of whether toadminister the shock to the victim than was used to determine whether topre-charge the defibrillator.

If a shockable rhythm does not exist at this later time and under thislater standard (though the standard may also be the same for decidingwhether to pre-charge and deciding whether to remove the safetyinterlocks and allow the shock actually to be delivered), the AEDinstructs the rescuer to continue chest compressions at box 434 suchthat the victim receives uninterrupted chest compressions. At box 435,the AED dissipates the charge (e.g., using one or more of the methodsdescribed herein) from the defibrillation device without delivering ashock to the victim if the device was pre-charged (e.g., at box 427).

If a shockable rhythm is observed, at box 430, the AED device determineswhether the defibrillator was pre-charged (e.g., at box 427) and chargesthe defibrillator if it was not previously pre-charged (or completes anystill-incomplete charging). At box 431, the AED device instructs therescuer to discontinue chest compressions (e.g., using one or more ofthe methods described herein). At box 432, the AED device delivers theshock and at box 432, the AED device instructs the user to resume chestcompressions. This initiates another CPR cycle during which a similarECG analysis will be performed.

FIG. 4C is a flow chart showing actions taken to charge a defibrillationdevice using different current levels based on the likelihood of ashockable rhythm being observed. One exemplary way to conserve power inan AED is to charge the AED device at a lower current over a longerperiod of time (e.g., over a period of at least 30 seconds), resultingin less of a drain on the batter power as compared to charging the AEDdevice to the same total charge using a higher current and a shorterperiod of time (e.g., over a period of at most 10 seconds). A percentagecalculated by dividing the lower charging current by the higher chargingcurrent can be greater than about 50% (e.g., greater than about 50%,greater than about 60%, greater than about 75%) and less than about 90%(e.g., less than about 90%, less than about 80%).

Charging the AED device over a longer period of time at a lower currentcan occur during the CPR interval because the typical CPR interval isbetween 2-5 minutes. Both charging the device at a lower current (thatis selected to permit full or substantially full charging during theavailable charging interval before a shock may be needed) and/or onlycharging the device if it is likely that a shock will be administered tothe victim can contribute to an extended battery life for the AEDdevice. Drawing less total current from the battery can provideadditional advantages such as enabling the use of a smaller battery (andthereby enabling a smaller and lighter AED) and/or enabling the use ofalternative power devices such as solar power and/or human generatedpower.

In one embodiment, a “crank” generator may be employed. Since the timeavailable to charge the defibrillator capacitor can be increased to asmuch as 3-10 minutes using the systems described herein, a 200 joulecapacitor only requires at most approximately a 1.5 watt power source,assuming a 3 minute charge duration and a high voltage flyback circuitryefficiency of 75%. Due to leakage of a typical film capacitor at maximumvoltage of approximately 2 Watts, a generator of 2.5-3 Watts would berequired. Such a power supply may be an external hand crank power supplyavailable commercially (SuperBattery with Crank Generator, Teledex,Inc., N.J.), or a built-in crank generator in the defibrillator with apower output sufficient to charge the defibrillator capacitor in theallotted time. As part of the generator, an additional energy storageelement will preferably be included, for instance a battery as containedin the Superbattery described above, or a so-called “ultracapacitor”,such as that manufactured by Maxwell Technologies (San Diego), forinstance the 350 Farad, part number BCAP0350 E270 T11. Theultracapacitor is used to maintain power for the low-voltage circuitrysuch as signal amplifiers and digital processing circuitry when therescuer has stopped providing mechanical energy to the generator. Themechanical energy for the generator may alternatively be contained in astructure positioned on the patient's sternum, which will be compressedduring cardiopulmonary resuscitation. Currently, devices existcommercially (CPR-STATPADZ, ZOLL Medical, Chelmsford, Mass.) whichmeasure the performance of the rescuer doing chest compressions bymeasuring the compression depth via an accelerometer sensor within alow-profile housing positioned under the rescuers hands while they arecompressing the patient's sternum during CPR. The housing mayadditionally be constructed to flexibly deform during sternalcompressions, thus causing motion of the actuator of a generator, forinstance a linear motion electric power generator as described in U.S.Pat. No. 5,818,132. A typical patient requires approximately 100 poundsof force to depress the sternum to the required depth of 2 inches, asper the American Heart Association recommendations. Thus, by allowingfor a deformation of the housing of 0.5-1 inches would increase thecompression depth of the rescuer to 2.5-3 inches to achieve the samesternal depth of 2 inches, but would provide the requisite 2.5-3 Wattsof necessary power, assuming a generator efficiency of 40%.Alternatively, the housing may be a spring-loaded two piece housing withaccelerometer and generator contained within the housing, the upperportion of the generator actuator affixed to the upper portion of thehousing, the generator and the lower portion of the actuator affixed tothe lower housing, and power generated when the spacing between theupper and lower housings is changed.

In another embodiment, the lid of the AED might be surfaced with a solarcell, thus providing approximately 100 square inches of availablesurface area. Standard, commercially available amorphous Silicon crystalcells currently provide approximately 45 milliwatts per inch squared.This power can be doubled by employing a more expensive crystalline cellas well as alternative structures. Thus, the solar cell would be able toprovide 4-10 Watts of power, which is more than sufficient for thesystems described herein. As with the human powered generator approach,an electrical energy storage element would be included, such as anultracapacitor, in addition to the defibrillator capacitor, for poweringthe analog and digital low-voltage electronics, if for instance a shadowfrom the rescuer passes in front of the solar cells during device use.Thus, even with batteries that have failed or whose performance hasdegraded to the point that they are unable to power the defibrillator,it is now possible to have a backup power source for use in emergencies,not currently available with existing technology. In the preferredembodiment, a fail-safe switch, relay or transistor would be employedthat would disconnect the failed batteries from the electronics, so thatpower would not be diverted from the generator or solar cell by thebatteries during operation.

Because the defibrillator capacitor can be charged over a significantlyincreased period of time, the peak charging current is significantlydecreased by a factor of ten or more. This allows for significantlysmaller batteries to be used to power the defibrillator. In general, thebatteries can include one or more primary cells and/or one or moresecondary (e.g., rechargeable) cells. Examples of significantly smallerbatteries that can be used to power the defibrillator include anybattery (or combination of multiple batteries) with a relatively lowpower output of, for example, less than about 10 W (e.g., less thanabout 10 W, less than about 7 W, less than about 5 W, less than about 4W, less than about 3 W). In some examples, the power output can begreater than about 2.5 W and less than 10 W (e.g., between about 2.5 Wand about 10 W, between about 2.5 W and about 7 W, between about 2.5 Wand about 5 W, between about 2.5 W and about 4 W, between about 2.5 Wand about 3 W). In one particular example, the current ZOLL AEDPlus usesten lithium CR123 commercial batteries to power the defibrillator, at asignificant size, weight and cost expense. With the systems and chargingmethods described herein, this can be reduced to 1, or at most, 2 CR123batteries. In addition, it is now possible to use even smaller alkalinebatteries, such as a standard commercially-available ‘C’ size alkalinecell.

At box 436, while chest compressions are being administered, the AEDanalyzes an ECG signal (e.g., as described in U.S. Pat. No. 7,565,194)and at box 437, the AED determines if a shockable rhythm is likely to bepresent in the victim at the end of the CPR interval. While the CPRinterval will continue regardless of the outcome of the analysis, thedetermination is used to decide whether to begin charging thedefibrillator device.

If a shockable rhythm is not likely to be present in the victim at theend of the CPR interval, the AED continues to receive and analyze theECG signals. At box 439, near the end of the CPR cycle, the AED performsa final analysis of the ECG signal to determine whether a shockablerhythm exists. The analysis may also continue until a shockable rhythmis present.

In contrast, if the system determines that a shockable rhythm is likelyto exist (either initially or upon further monitoring and analysis), atbox 438, the AED device begins pre-charging the defibrillation device ata low charging current. In other examples, the charging current can bebased on the length of time remaining in the CPR interval. For example,a charging current can be selected such that the device will be fullycharged at the end of the CPR interval. This may result in the chargingoccurring at a low rate over an extended period of time (e.g., over aperiod of time greater than about 30 seconds, over a period of timegreater than about 45 seconds, over a period of time greater than about1 minute). For example, if a shockable rhythm is determined initially,the charging rate may be relatively low, whereas if there was no initialshockable rhythm but the device senses a shockable rhythm later in thechest compression cycle, the charging rate may be relatively fast. Thischarging occurs while the rescuer is administering the CPR chestcompressions (though some may occur after the end of the provision ofCPR chest compressions, though not enough that it would create ansubstantial effect on the timing of the CPR).

At box 439 near the end of the CPR cycle, the AED device performs afinal analysis of the ECG signal, and at box 440, the AED devicedetermines whether a shockable rhythm exists. If a shockable rhythm doesnot exist, the AED instructs the rescuer to continue chest compressionsat box 450 such that the victim receives uninterrupted chestcompressions. At box 452, the AED dissipates the charge (e.g., using oneor more of the methods described herein) from the defibrillation devicewithout delivering a shock to the victim if the device was pre-charged(e.g., at box 438).

If a shockable rhythm is observed, at box 441, the AED device determineswhether the defibrillator has reached a full level of charge and chargesthe defibrillator to the full level of charge (if needed) at a highcurrent. For example, while the pre-charging can occur at a low currentover an extended period of time, charging to reach the full charge ifthe device is not fully charged in time (or charging if not pre-charged)can occur at a high current and during as short of period as ispractical.

At box 444, the AED device instructs the rescuer to discontinue chestcompressions (e.g., using one or more of the methods described herein).At box 446, the AED device delivers the shock and at box 448, the AEDdevice instructs the user to resume chest compressions. This initiatesanother CPR cycle during which a similar ECG analysis will be performed.

FIG. 4D is a flow chart showing actions taken to adaptively charge adefibrillation device to a level (e.g., a desired total voltage orcharge) selected based on ECG analysis. For example, a level of chargefor the defibrillation device (and a total amount of charge delivered tothe victim) can be adaptively determined based on factors related to theECG analysis such as the amplitude, frequency of the ECG signal, and/oran AMSA value. For example, if a victim is experiencing VF with a highamplitude ECG signal, only a low level of energy in the shock may beused. In contrast, in situations where it is not likely that conversionto a perfusing rhythm will occur with only a low energy shock such assituations in which the ECG signal exhibits a low amplitude, then thedefibrillation device can be charged to a higher energy level.

In some implementations, an amplitude magnitude spectrum area (AMSA)value can be used to determine how to charge the defibrillation deviceand when to administer a defibrillation shock. For example, a high AMSAvalue is believed to be correlated to a high likelihood of conversion toa perfusing rhythm. The AMSA value can be monitored and the level ofshock and/or length of time chest compressions are administered can bemodified based on a threshold AMSA value and/or trends observed in theAMSA value. For example, a shock could be administered when a change(e.g., a decrease) in the AMSA value is observed by systems provided inan AED device. The AMSA value can also be used to determine the rate incharging the defibrillator. For example, an AMSA number that isassociated with an accuracy level of 70% or greater (e.g., 70%, 80%,90%) in predicting a successful conversion can be associated with thefastest possible rate in charging the defibrillator; The lower value theAMSA number is, the rate of charging is set to (e.g., half speed incharging when an AMSA number associated with an accuracy level of 50% isobserved).

In FIG. 4D at block 462, while chest compressions are beingadministered, the AED device analyzes an ECG signal, and at box 464, theAED device determines if a shockable rhythm is likely to be present inthe victim at the end of the CPR interval. If a shockable rhythm is notlikely to be present in the victim at the end of the CPR interval, theAED instructs the rescuer to continue chest compressions for another CPRinterval at box 468 and continues to receive and analyze the ECGsignals. If the system determines that a shockable rhythm is likely toexist, at box 466, the AED device determines a level of charge based onan analysis of the ECG signal. For example, the level of charge or therate of charging can be based on an amplitude of the ECG signal, afrequency of the ECG signal, and/or and AMSA value of the ECG signal.The level of charge can vary from a low charge to a high charge. Ingeneral, if the AMSA value is used, the level of charge is proportionalto the AMSA value such that the device is charged to a higher level ifthe AMSA value is higher. At box 470, the AED charges the defibrillationdevice to the determined level of charge. The rate of charging can alsovary from a slow charging rate to a fast charging rate: for example, ifthe AMSA value is used, the charging rate can be proportional to theAMSA value such that the device is charged faster if the AMSA value ishigher.

Alternatively, other measures of the underlying energy status orperfusion state of physiologic tissue (ESPPT) of the victim may beutilized instead of AMSA is just described. These alternative measuresof ESPPT may include near-infrared spectroscopy that has been shown tobe able to measure tissue pH as well as mitochondrial energy status.Alternative ESPPT sensors may include fiber optic pO2 and pCO2 sensorssuch as that described by Cajlakovic and colleagues in “Simultaneouslymonitoring of tissue O2 and CO2 partial pressures by means ofminiaturized implanted fiber optical sensors” (IEEE Sensors 2009Conference). Location for sensing ESPPT is preferably in the buccalcavity, which has been shown in previous research for traumatic arrest,shock and cardiac arrest to provide good correlation to vital organphysiologic status. Other locations may be the tragus of the ear,intravenously either arterial or venous, or via fiberoptic needle probeinto skeletal muscle tissue.

At box 472, near the end of the CPR interval, the AED device performs afinal analysis and determines (box 474) if a shockable rhythm ispresent. If a shockable rhythm does not exist, the AED instructs therescuer to continue chest compressions at box 482 such that the victimreceives uninterrupted chest compressions. At box 483, the AEDdissipates the charge (e.g., using one or more of the methods describedherein) from the defibrillation device without delivering a shock to thevictim.

If a shockable rhythm is observed, at box 476, the AED instructs therescuer to discontinue chest compressions (e.g., using one or more ofthe methods described herein). At box 478, the AED device delivers theshock and at box 480, the AED device instructs the user to resume chestcompressions.

Other data besides ECG data may be included as part of the determinationof whether a shockable rhythm exists and may be incorporated into theanalysis algorithm, for instance pulse oximetry, capnography,respiration, impedance cardiography, and blood pressure measurements. Atleast some of the data may remain in the time domain without any Fourieror other transform method being performed on it. Pulse oximetry,impedance cardiography, and blood pressure measurements may be used toaugment the ECG to determine if a pulse is present. Capnography may beused to determine the overall effectiveness of cardiopulmonaryresuscitation. The additional measures can also include measurement ofvelocity or acceleration of chest compression during chest compressionsaccording to the techniques taught by U.S. Pat. No. 7,220,335, Methodand Apparatus for Enhancement of Chest Compressions During ChestCompressions, the contents of which are hereby incorporated by referencein their entirety and U.S. patent application Ser. No. 11/430,579 titledECG rhythm advisory method the contents of which are hereby incorporatedby reference in their entirety.

In some embodiments, the cross-correlation between the ECG signal (withCPR artifact) and the CPR signal (in the form of compressionacceleration, velocity, or displacement) can be calculated. Based on thestrength of the cross-correlation between the ECG signal and the CPRsignal, the system can select an appropriate analysis method to removethe artifacts from the ECG signal and determining if a shockable rhythmexists in the ECG signal. For example, a high cross-correlation valuebetween the ECG signal and the CPR signal indicates that the majority ofthe artifact is from the chest compression and thus an analysis methoddesigned for ECG with CPR artifact may be more reliable than otheranalysis methods. Alternatively, a low cross-correlation value typicallyindicates that there is strong non-CPR-related artifact in the recordedECG signal.

FIGS. 5A and 5B illustrate an example of the observed ECG signal (FIG.5A) showing strong cross-correlation with the CPR acceleration signal(FIG. 5A), which indicates that the ECG signal is free from non-CPRnoise. The strong cross correlation can be observed based on thesimilarity in the shape of the CPR signal and the ECG signal. The crosscorrelation can be computed automatically during the analysis of the ECGsignal.

As noted above, a low cross-correlation value between the ECG signal andthe CPR signal typically indicates that there is strong non-CPR-relatedartifact in the recorded ECG signal. With the presence of thenon-CPR-related artifact, the ECG analysis performed during CPR may beless reliable (or may not be reliable). Due to the lesser reliability ofthe ECG analysis, the system can utilize a longer period of CPR-freetime in a re-confirmation analysis (e.g., a longer analysis period canbe utilized after the cessation of CPR and prior to the determination ofwhether a shockable rhythm exists). FIGS. 6A and 6B illustrate anexample of the observed ECG signal (FIG. 6A) with weak cross-correlationwith the CPR acceleration signal (FIG. 6B). This indicates that the ECGhas strong non-CPR noise and a longer of re-confirmation analysis periodcan be used.

The information processing technique can include but is not limited tosimple combining rules or math, neural networks, expert systemsincorporating fuzzy or standard logic, or other artificial intelligencetechniques. For example, multiple factors can be combined to make adetermination of whether to defibrillate. In some situations, even if ashockable rhythm exists (e.g., as determined based on the ECG analysis)the AED device may not recommend delivering the shock to the patientbecause one or more other factors suggest that another treatment wouldlikely be more effective. For example, if a shockable rhythm exists butthe quality of CPR chest compressions as measured based on one or moreof the velocity, acceleration, or depth of the compressions is low, thenthe AED device could recommend continuing chest compressions to increaseblood circulation rather than stopping the chest compressions to deliverthe shock.

In some embodiments, the AED device can combine different measures andoutput results related to the desirability of defibrillation and/or theeffectiveness of the chest compressions being delivered by the rescuer.Exemplary outputs can include statements such as “strong need fordefibrillation,” “weak need for defibrillation,” “faster chestcompressions needed,” or “additional chest compressions needed.”

In some embodiments, the AED device can deliver the defibrillation shockduring the chest compression cycle (e.g., while the rescuer isdelivering the chest compressions). For example, the AED can synchronizeof the defibrillation shock to the chest compression cycle. Delivery ofthe defibrillation shock during the early portion (approximately thefirst 300 milliseconds) of the decompression (diastolic) phase of thechest compression cycle can improve the likelihood of success of thedelivered shock. The decompression phase begins when the rescuer reducescompression force on the chest, allowing the chest to rise, and theheart to expand. The AED device can detect chest compression phase andtiming information indicative of the start of the decompression phaseand initiate delivery of the electromagnetic therapy within 300milliseconds of the start of the decompression phase. In someembodiments, delivery of electromagnetic therapy can be initiated within25-250 milliseconds of the start of the decompression phase. Circuitryand processing for the detection of chest compression phase timinginformation can include a pressure sensor and/or an accelerometer.Exemplary methods for synchronizing defibrillation with chestcompression phase are described in U.S. patent application Ser.12/263,813 titled Synchronization of Defibrillation and ChestCompressions, the contents of which are hereby incorporated by referencein their entirety.

Large self-adhesive electrode pads (˜5″ in diameter) are typically usedto deliver defibrillation therapy to patients. The pads also provide ECGmonitoring through the conductive surfaces that deliver therapy. In oneimplementation, additional small (˜0.5″ diameter) ECG electrodes can beintegrated into the large pads.

In one embodiment, the two small ECG electrodes and large pads areconfigured such that there at least two mutually orthogonal ECG leadsare generated. The vector sum of these leads generates a trajectory overtime. The same methods for trajectory analysis described above may beused to analyze this trajectory as well.

Additionally, the defibrillator may take the form of a wearabledefibrillator such as the LifeVest, manufactured by ZOLL Medical(Chelmsford, Mass.).

Many other implementations other than those described may be employed,and may be encompassed by the following claims.

What is claimed is:
 1. An external defibrillator comprising: aprocessor; a defibrillator pulse generator operatively connected to theprocessor and configured to generate a defibrillating shock; andelectrode pads configured to be operatively connected to thedefibrillator pulse generator and the processor to deliver thedefibrillating shock from the defibrillator pulse generator to thepatient, the electrode pads further configured to deliver one or moreECG signals from the patient to the processor, wherein the processor isprogrammed to: analyze one or more electrocardiogram (ECG) signals fromthe patient during delivery of chest compressions to the patient;determine appropriateness of delivering a shock to the patient based onthe analysis of the one or more ECG signals during the delivery of chestcompressions of a CPR interval; determine that the chest compressions ofthe CPR interval have been completed; analyze one or more ECG signalsacquired in an absence of chest compressions within about 5 secondsafter cessation of the chest compressions of the CPR interval to confirmthe appropriateness of delivering the shock to the patient; and providean indication on a display screen of a recommendation of providing ashock to the patient based on the determined appropriateness ofdelivering the shock to the patient.
 2. The external defibrillator ofclaim 1, wherein the processor is programmed to provide the indicationon the display screen of the recommendation of providing the shock tothe patient based on the confirmed appropriateness of delivering theshock to the patient from the analysis of the one or more ECG signalsacquired in the absence of chest compressions.
 3. The externaldefibrillator of claim 1, wherein the analysis of the one or more ECGsignals acquired in an absence of chest compressions occurs within about3 seconds after the cessation of the chest compressions of the CPRinterval.
 4. The external defibrillator of claim 1, wherein the analysisof the one or more ECG signals acquired in an absence of chestcompressions occurs within about 1 second after the cessation of thechest compressions of the CPR interval.
 5. The external defibrillator ofclaim 1, wherein a duration of the CPR interval is preset in theprocessor.
 6. The external defibrillator of claim 5, wherein theduration of the CPR interval is about two minutes.
 7. The externaldefibrillator of claim 1, wherein the processor is programmed to provideinstructions to cease chest compressions once the CPR interval has beencompleted.
 8. The external defibrillator of claim 7, wherein theinstructions comprise an output for a rescuer to cease manualcompressions once the CPR interval has been completed.
 9. The externaldefibrillator of claim 1, wherein the defibrillator pulse generatorcomprises a capacitor electrically connected to an electrical energystorage source.
 10. The external defibrillator of claim 9, wherein theprocessor is programmed to charge the capacitor during delivery of thechest compressions of the CPR interval to the patient.
 11. The externaldefibrillator of claim 9, further comprising one or more safetyinterlocks to prevent accidental discharge of the capacitor duringcharging of the capacitor.
 12. The external defibrillator of claim 9,wherein the processor is programmed to cause the capacitor to dissipatea charge if the analysis of the one or more ECG signals acquired in theabsence of chest compressions does not confirm the appropriateness ofdelivering the shock to the patient.
 13. The external defibrillator ofclaim 9, wherein the processor is programmed to, based on the analysisof the one or more ECG signals, determine whether to charge thecapacitor or to provide instructions to continue the chest compressionsof the CPR interval without charging the capacitor.
 14. The externaldefibrillator of claim 9, wherein the processor is programmed to, basedon the analysis of the one or more ECG signals, determine whether toprovide instructions to continue the chest compressions of the CPRinterval.
 15. The external defibrillator of claim 1, wherein theelectrode pads comprise adhesive material for adhering to the patient.16. The external defibrillator of claim 1, wherein determining theappropriateness of delivering the shock to the patient during deliveryof the chest compressions of the CPR interval to the patient comprisesdetermining a level of certainty of whether the shock is appropriate,the level of certainty being one of at least a low level of certaintyand a high level of certainty.
 17. The external defibrillator of claim16, wherein the processor is configured to provide the indication of therecommendation of providing the shock to the patient immediately aftercessation of chest compressions when reaching a high enough level ofcertainty of appropriateness of delivering the shock.
 18. The externaldefibrillator of claim 16, wherein the processor is configured toconfirm the appropriateness of delivering the shock to the patient basedon the analysis of the one or more ECG signals acquired in the absenceof chest compressions when the level of certainty of appropriateness ofdelivering the shock is insufficient.
 19. The external defibrillator ofclaim 1, wherein a duration of the CPR interval is variable based onanalysis of the one or more ECG signals by the processor.
 20. Theexternal defibrillator of claim 1, wherein the processor is furtherprogrammed to control the defibrillator pulse generator to deliver theshock to the patient based at least in part on the confirmation of theappropriateness of delivering the shock to the patient.
 21. The externaldefibrillator of claim 1, further comprising a therapy button configuredto cause the defibrillator pulse generator to deliver the defibrillatingshock to the patient.
 22. The external defibrillator of claim 21,further comprising a safety interlock for controlling enablement of thetherapy button that causes the defibrillator pulse generator to deliverthe defibrillating shock to the patient.
 23. The external defibrillatorof claim 22, wherein the processor is programmed to disable the safetyinterlock so as to enable the therapy button to cause the defibrillatorpulse generator to deliver the defibrillating shock to the patient. 24.The external defibrillator of claim 23, wherein the processor isprogrammed to disable the safety interlock based on the confirmedappropriateness of delivering the shock to the patient.
 25. The externaldefibrillator of claim 1, further comprising: circuitry for detection ofchest compressions delivered to the patient.
 26. The externaldefibrillator of claim 25, wherein the processor is programmed todetermine that the chest compressions of the CPR interval have beencompleted based on a signal from the circuitry for detection of chestcompressions delivered to the patient.
 27. A method for providingelectrical therapy to a patient, the method comprising: analyzing one ormore electrocardiogram (ECG) signals from the patient during delivery ofchest compressions of a CPR interval to the patient; determiningappropriateness of delivering a shock to the patient based on theanalysis of the one or more ECG signals during the delivery of the chestcompressions; determining that chest compressions of the CPR intervalhave been completed; after the chest compressions of the CPR intervalhave been completed, analyzing one or more ECG signals to confirm theappropriateness of delivering the shock to the patient within about 5seconds after a rescuer has completed the chest compressions of the CPRinterval; and providing an indication on a display device of arecommendation of providing a shock to the patient based on thedetermined appropriateness of delivering the shock to the patient. 28.The method of claim 27, further comprising setting a duration of the CPRinterval.
 29. The method of claim 28, wherein the duration of the CPRinterval is preset.
 30. The method of claim 29, wherein the duration ofthe CPR interval is about two minutes.
 31. The method of claim 27,further comprising providing an indication to the rescuer that the CPRinterval is completed.